Question

The effective length of a magnet is \(31.4\) cm and its pole strength is \(0.8\) A m. The magnetic moment, if it is bent in the form of a semicircle, is

• A. \(0.12\ \text{A m}^2\)
• B. \(0.16\ \text{A m}^2\)
• C. \(1.2\ \text{A m}^2\)
• D. \(1.6\ \text{A m}^2\)

Hint:

For curved magnets, magnetic moment depends on the separation between poles, not the arc length.

Answer 1

The Correct Option is B

Step 1: Understand effective length relation.
Effective length \(= \pi r\).
\[ r = \frac{31.4}{\pi} = 10\ \text{cm} = 0.1\ \text{m} \]
Step 2: Calculate magnetic moment.
Magnetic moment is given by:
\[ M = m \times (2r) \]
Step 3: Substitute values.
\[ M = 0.8 \times 0.2 = 0.16\ \text{A m}^2 \]
Step 4: Conclusion.
The magnetic moment is \(0.16\ \text{A m}^2\).